File in c S-Teacher

1. FILE HANDLING

2. Introduction
Files are places where data can be stored
permanently.
Some programs expect the same set of data to be
fed as input every time it is run.
Cumbersome.
Better if the data are kept in a file, and the program
reads from the file.
Programs generating large volumes of output.
Difficult to view on the screen.
Better to store them in a file for later viewing/
processing

3. Basic File Operations
Opening a file
Reading data from a file
Writing data to a file
Closing a file

4. Opening a File
A file must be “opened” before it can be used.
FILE *fp;
:
fp = fopen (filename, mode);
fp is declared as a pointer to the data type FILE.
filename is a string - specifies the name of the file.
fopen returns a pointer to the file which is used in all
subsequent file operations.
mode is a string which specifies the purpose of opening
the file:
“r” :: open the file for reading only
“w” :: open the file for writing only
“a” :: open the file for appending data to it

5. Closing a File
After all operations on a file have been
completed, it must be closed.
Ensures that all file data stored in memory buffers are
properly written to the file.
General format: fclose (file_pointer) ;
FILE *xyz ;
xyz = fopen (“test”, “w”) ;
…….
fclose (xyz) ;

6. Read/Write Operations on Files
The simplest file input-output (I/O) function are getc and
putc.
getc is used to read a character from a file and return it.
char ch; FILE *fp;
…..
ch = getc (fp) ;
getc will return an end-of-file marker EOF, when the end of the
file has been reached.
putc is used to write a character to a file.
char ch; FILE *fp;
……
putc (c, fp) ;

7. main() {
FILE *in, *out ;
char c ;
in = fopen (“infile.dat”, “r”) ;
out = fopen (“outfile.dat”, “w”) ;
while ((c = getc (in)) != EOF)
putc (toupper (c), out);
fclose (in) ;
fclose (out) ;
}

8. Basic operations of files(Contd.)
We can also use the file versions of scanf and printf,
called fscanf and fprintf.
General format:
fscanf (file_pointer, control_string, list) ;
fprintf (file_pointer, control_string, list) ;
Examples:
fscanf (fp, “%d %s %f”, &roll, dept_code, &cgpa) ;
fprintf (out, “nThe result is: %d”, xyz) ;

9. Command line argument
Command line arguments are parameters supplied to a
program, when the program is invoked.
How do these parameters get into the program?
Every C program has a main function.
main can take two arguments conventionally called argc and
argv.
Information regarding command line arguments are passed to
the program through argc and argv.

10. Command line argument
Command line arguments are parameters supplied to a
program, when the program is invoked.
How do these parameters get into the program?
Every C program has a main function.
main can take two arguments conventionally called argc and
argv.
Information regarding command line arguments are passed to
the program through argc and argv.